1. Field of the Invention
The present invention relates to a pneumatic tire with an improved belt structure being capable of reducing the tire weight without sacrificing the steering stability, ride comfort, durability and the like.
2. Description of Related Art
In pneumatic tires especially radial tires, a tread reinforcing belt, which is composed of cords each made of twisted steel filaments, is widely used.
In recent years, on the other hand, there is a great demand for a lightwaight tire to save energy.
In order to reduce the amount of steel in a tread reinforcing belt, a trial has been made using a relatively thick steel filament as a cord because such a monofilament cord has a less steel amount than a multifilament cord when the bending rigidity of the monofilament cord is set at the same degree as the multifilament cord. However, the elongation of such monofilament cord when loaded is very small and liable to break. Thus, the durability of the belt is not good, and the cornering force becomes insufficient and the steering stability is lowered. If the thickness is increased in order to avoid breaking, the bending rigidity suddenly increases, and ride comfort is greatly decreased. Thus, it is very difficult to use a monofilament cord in a tread reinforcing belt.
It is therefore, an object of the present invention to provide a pneumatic tire, in which a filament having a specific size being waved in a specific manner is used as a belt cord to achieve a weight reduction without sacrificing the durability, ride comfort, steering stability and the like.
According to the present invention, a pneumatic tire comprises a belt disposed radially outside a carcass in a tread portion, the belt comprising two cross plies of monofilament metallic cords laid at angles of from 15 to 30 degrees with respect to the circumferential direction of the tire, each monofilament cord composed of a waved single filament, the filament having a circular sectional shape having a diameter in a range of from 0.40 to 0.50 mm, or alternatively a non-circular sectional shape having an aspect ratio in a range of from 0.65 to 0.95 and a cross-sectional area in a range of 0.09 to 0.20 sq.mm.
Embodiments of the present invention will now be described in detail in conjunction with the accompanying drawings.